Among known pull-on garments is included a disposable pull-on diaper including an absorbent assembly and an outer cover assembly defining the exterior surface of the garment and having its front body portion and rear body portion connected to each other along their lateral side edges to form a pair of side seams.
In removing a disposable pull-on diaper from a wearer, the diaper is usually torn open into a front body portion and a rear body portion in the side seam. In order to quickly remove a diaper from a body of the wearer at the time of changing the diaper after use, the side seams are preferably configured to be easily torn open. With regard to tearability of side seams, Patent Literature 1 proposes providing side seams with a combination of three levels of bonding strength so as to improve the tearability as well as to maintain a bonding strength enough to prevent tear during use of the diaper.
In the conventional manufacture of absorbent articles such as disposable diapers and sanitary napkins, a heat roller unit has been used widely to join superimposed sheets, and side seams are usually formed by the heat roller unit as will be described later. Laser welding is another known method for joining superimposed sheets. For example, Patent Literature 2 discloses a method for uniting a continuous stack of sheets by fusion bonding, the method comprising transporting a continuous stack of sheets on a rotating drum while deforming the sheets in conformity to the peripheral surface of the drum, the drum having a laser beam transmissive window, and directing a laser beam from the inside of the rotating drum to the moving stack of sheets.
A disposable pull-on diaper is generally manufactured through the steps of making a continuous length of diaper (also referred to as a continuous diaper web) having a plurality of diapers connected to each other in one direction (machine direction), connecting the superimposed front and rear body portions of the outer cover assembly at positions corresponding to side seams by a bonding means, such as a heat roller unit, and severing the thus bonded portions by a cutting means, such as a cutter, to obtain individual diapers. The side seams of the thus manufactured conventional disposable pull-on diapers are butt-type seams formed by superimposing both lateral side edge portions of the front and rear body portions in a face-to-face relationship. Because the side edge of the butt-type side seam protrudes outwardly from the neighboring part of the diaper, the side seam is readily recognizable by the naked eye.
Patent Literature 3 below discloses a disposable pull-on diaper which is produced by bonding both side edges of the front and rear body portions of a non-stretch backsheet while leaving a leg elasticized portion unbonded to form a slit in each side seam.